Radio telemetry of butterflies: practical insights and critical tag-weight thresholds

Background: Radio telemetry offers new opportunities for studying the movement of insects. One important prerequisite for using radio tags to study butterfly movement ecology is that tag weight and attachment do not significantly affect butterfly flight performance. Despite recent applications of telemetry in butterflies, a systematic evaluation of tag-to-body-weight thresholds for successful tagging has been lacking. Methods: We tested ultra-light radio tags (0.13 g) on 117 individuals of 18 butterfly species under greenhouse and field conditions. Tag-to-body-weight ratios ranged from 5.6% to 77.8%. We used generalized linear mixed-effects models to identify predictors of flight success and used ROC analysis to determine the critical tag-to-body-weight threshold. Tag retention was also compared between thoracic and abdominal attachment sites. Results: We found that a threshold of approximately 20% of body weight marks a critical point beyond which flight performance declines significantly. Abdominal tag attachment proved more reliable and stable than thoracic attachment, with lower detachment rates. Conclusions: This study presents the first comprehensive evaluation of tag-to-body-weight thresholds and attachment methods in butterfly telemetry. The results provide practical guidance for planning radio telemetry studies of butterflies and for conducting further methodological research, such as into the effects of tagging on butterfly behavior, body condition, survival, and reproduction.